In fabricating micro-electronic semiconductor device components and the like on a semiconductor wafer (chip), e.g., of silicon (Si), to form an integrated circuit (IC), etc., various conductive, e.g., metal or poly silicon, layers and dielectric (insulation), e.g., oxide, layers are provided in selective sequence on the wafer. To maximize device component integration (connection) in the available wafer area to fit more components in the same area, increased IC miniaturization is utilized. Reduced pitch dimensions permit denser packing of components per very large scale integration (VLSI) technique, e.g., at sub-micron dimensions, i.e., below 1 micron ({fraction (1/25,400)} inch) or 1,000 nanometers (nm) or 10,000 angstroms (A), and especially per ultra large scale integration (ULSI) technique, e.g., at sub-quarter micron dimensions, i.e., below 0.25 micron (250 nm).
One type of wet chemical planarization process used in the IC fabrication of a semiconductor wafer, or for planarizing any particular substrate as work piece, concerns the chemical mechanical polishing (CMP) of a surface of the work piece against a polishing pad during relative periodic movement, i.e., frictional sliding contact, therebetween, such as with a caustic (basic pH, e.g., pH 7.5-14) slurry for oxide CMP, or an oxidizing (acidic pH, e.g., pH 1-6.5) slurry for metal CMP. The slurry typically contains finely divided abrasive particles, e.g., colloidal silica (SiO2), alumina (Al2O3), ceria (CeO2), zirconia (ZrO2), titania (TiO2), and rare earth oxides other than ceria, and the like, in a polishing liquid such as deionized water.
The slurry is typically a suspension of such abrasive particles in a polishing liquid such as an aqueous potassium hydroxide (KOH) solution where the polishing liquid is of basic pH, or such as an aqueous sulfuric acid (H2SO4) solution where the polishing liquid is of acidic pH. The slurry can contain other components such as electrolyte substances, e.g., electrolytes, i.e., (i) inorganic electrolytes and (ii) organic electrolytes, as well as (iii) polyelectrolytes, to enhance the CMP operation, e.g., to facilitate removal of polishing debris particles, i.e., swarf, generated during the planarizing.
On the one hand, electrolytes are substances that dissociate into ions in water, and include (i) inorganic electrolytes and (ii) organic electrolytes. (i) Inorganic electrolytes are water soluble ionizable salts of inorganic acids and bases such as water soluble alkali metal (e.g., sodium, potassium, lithium and cesium), alkaline earth metal (e.g., calcium, magnesium, strontium and barium), and ammonium, salts, including water soluble halides (i.e., chlorides, bromides, iodides and fluorides), nitrates, sulfates (i.e., excluding water insoluble sulfates such as calcium sulfate, barium sulfate and strontium sulfate), and the like, thereof. (ii) Organic electrolytes are water soluble ionizable organic compounds such as amino acids, amines, amides, pyridinium halides (e.g., chloride), ethylene glycols, ethylene oxides, and the like.
On the other hand, (iii) polyelectrolytes are polymers producing large chain type ions in solution, that can carry positive or negative groups along the polymer chain, and are described more fully hereinafter.
The frictional sliding contact polishing action between the polishing pad and wafer (or other substrate) serves to remove by a combination of chemical etching and mechanical abrasion or erosion a thin layer of material, e.g., 1 micron or less in thickness, so as to obtain planarization of the wafer (or other substrate) surface. Close control of the slurry flow rate, its concentration, temperature and pH are necessary to attain in a reproducible manner a uniform removal rate per the CMP operation.
The usual CMP process involves dispensing the slurry from a stationary overlying tube dropwise onto a polishing pad of a moving, e.g., rotating, table (platen), such as one which rotates about a stationary platen axis and against which the work piece, e.g., wafer or other substrate, which is usually carried by a retaining ring, makes frictional contact while the work piece and ring move, e.g., rotate and oscillate, relative to the platen. The work piece is normally positioned in a medial aperture of the retaining ring. Since the position of the work piece relative to the platen varies during wafer movement, e.g., rotation and oscillation, the slurry dispensing tube is always spaced a minimum clearance distance from the work piece.
Consequently, different portions of the wafer or other substrate necessarily encounter dispensed slurry droplets having different chemical constitution. This depends on the continuously varying distance between the relative position of movement, e.g., rotation and oscillation, of the wafer or other substrate, i.e., as work piece, and in particular of its leading and trailing edges during movement, e.g., oscillation, and the position of the, e.g., centrifugally outwardly, travelling slurry droplets dispensed onto the, e.g., rotating, platen from the stationary tube. As a result, the amount and chemical constitution of the slurry at the local polishing site of the wafer or other substrate work piece is inherently non-uniform, leading to non-uniformity of the CMP operation.
Also, some slurry on the polishing pad is pushed off the platen by the retaining ring and wafer or other substrate work piece arrangement, which is normally pressed under mechanical pressure (down force) against the polishing pad. This loss of slurry constitutes wastage which increases operating costs. By its continuous sliding contact relation with the polishing pad, the wafer or other substrate work piece necessarily impedes flow of slurry to the central area of the surface thereof being polished. This can cause poor center-to-edge uniformity, further detracting from the uniformity of the CMP operation.
Moreover, since the slurry constitutes a physical suspension of solid abrasive particles in a liquid, its components must be premixed in a storage vessel or freshly mixed immediately prior to delivery onto the polishing pad, so as to provide the abrasive particles in desired uniform suspension therein. If the components are premixed, the storage lifetime of the slurry is a limiting factor, especially due to the potential vulnerability of the slurry to agglomeration of the abrasive particles, e.g., of ceria, with other components in the slurry, e.g., electrolytes or polyelectrolytes. On the other hand, if the components are freshly mixed immediately prior to delivery onto the polishing pad, the system must include sophisticated pumps to meter the slurry in a precisely controlled flow.
The above prior art drawbacks cause adverse variation in the local removal rate of wafer or other substrate work piece material from different parts of the work piece due to variation in the amount and chemical constitution of the slurry coming into contact with the work piece surface being polished. This diminishes the degree of within-work piece uniformity. Also, slurry wastage increases its consumption rate and cost.
Some of these drawbacks are overcome by providing the polishing pad as a fixed abrasive pad in which the abrasive particles are embedded, being distributed in a binder material as matrix, e.g., a cured polymer resin, such that the polishing liquid forms a slurry-less liquid which only contains chemical components such as caustic (basic) or oxidizing (acidic) additives, plus auxiliary components such as electrolytes or polyelectrolytes. Slurry-less CMP is effected such that during frictional sliding contact between the wafer or other substrate work piece and polishing pad under the lubricating action of the slurry-less polishing liquid and the down force of the work piece against the polishing pad, the binder material incrementally breaks down (abrades, erodes) and incrementally releases the embedded abrasive particles for direct polishing action thereat.
However, even in the case of slurry-less CMP, the chemical components in the polishing liquid are prevented from immediately and uniformly contacting the work piece surface being polished. This is because the flow of slurry-less polishing liquid is dispensed from a stationary location onto the moving, e.g., rotating, polishing pad and can only contact the surface of the work piece being polished when the moving, e.g., rotating and reciprocating, work piece reaches the point on the polishing pad at which the particular polishing liquid droplets are located.
Moreover, since the wafer or other substrate work piece is maintained in continuous frictional sliding contact with the polishing pad, only a portion of the deposited slurry-less polishing liquid droplets can pass under the work piece in the interface area between the work piece surface being polished and the polishing pad, and then only non-uniformly. This results in less efficient use of the available slurry-less polishing liquid, including the contemplated electrolyte or polyelectrolyte, and in turn increased wastage thereof.
Since the CMP operation generates contaminating debris particles constituting a combination of particles of abraded portions of the wafer or other substrate surface being polished, particles of abraded portions of the binder material of the slurry-less fixed abrasive particle polishing pad, and spent abrasive particles released from the binder material of the polishing pad and fractured and abraded under the CMP conditions, the excess polishing liquid cannot be recycled as is, nor would its purification to remove such contaminants be practicable.
Some examples of polishing pads and their production and CMP use are shown in the following prior art.
[1] U.S. Pat. No. 5,876,490, issued Mar. 2, 1999 to Ronay (“[1] Ronay-490”), which is incorporated by reference herein, discloses a polishing slurry, e.g., for CMP, containing colloidal (e.g., 30-200 nm, preferably 75-100 nm, particle size) abrasive particles, e.g., of silica (SiO2), alumina (Al2O3), zirconia (ZrO2) or ceria (CeO2), and 5-10% (of the weight of the abrasive particles) of a polyelectrolyte adsorbed on a fraction of the abrasive particles and having ionic moieties different from the ionic charge associated with the abrasive particles. The slurry is used to polish SiO2 (i.e., on a semiconductor wafer) such as for achieving planarity in regard to shallow trench isolation (STI), in connection with a polishing pad maintained in moving contact with the wafer.
Polyelectrolytes are noted as substances that contain poly ions, which are macro-molecules having a large number of ionic groups, and to preserve their electro-neutrality, the poly ion charges must be compensated by counter ions, typically ions of low molecular weight such as H+ or Na+. Unlike most uncharged polymers, polyelectrolytes usually are soluble in polar solvents, e.g., water. As to their protonation equilibria in aqueous solution, they can be classified as polyacids, as polybases, or as polyampholytes if both acidic and basic groups are present.
Per [1] Ronay-490, the ionizable or anchoring groups by which the poly ions can be bound to the polishing abrasive particles include acidic groups such as carboxyl groups, e.g., in poly(acrylic acid), poly(methacrylic acid), poly(methyl methacrylic acid), poly(maleic acid), or saturated or unsaturated poly(carboxylic acids); and basic groups including nitrogen containing groups, such as polymers with amino, amide, imide, vinyl pyridine, piperidine and piperazine derivatives, e.g., poly(ethylenimine). Particular ionizable chain molecules contemplated include (e.g., where the monomer unit n=5-200):
1. poly[—CH2—CH(COOH)—]n(acrylic acid)2. poly[—CH2—CH(CH3) (COOH)—]n(methacrylicacid)3. poly[—CH2−CH(SO3H)—]n(vinyl sulfonicacid)4. poly[—CH2—CH(COOH)—CH(COOH)—CH(COOH)—]n(acrylicacid-co-maleicacid)5. poly[—CH2—CH(NH2)—]n(vinyl amine)6. poly[—CH2—CH2—NH—]n(ethylenimine)7. poly[—CH2—CH(4-C5H4N)—]n(4-vinylpyridine)
[2] U.S. Pat. No. 5,968,280, issued Oct. 19, 1999 to Ronay (“[2] Ronay-280”), which is incorporated by reference herein, discloses the use of a post-CMP cleaning composition, e.g., aqueous solution, containing, e.g., 0.02-2.0% based on the total composition, of a polyelectrolyte, for cleaning a substrate surface (e.g., of a semiconductor wafer) after it has been subjected to CMP, e.g., with a polishing slurry of colloidal abrasive particles, such as alumina, silica, zirconia or ceria, so as to remove contaminant particles such as polishing debris particles from the surface. The polyelectrolyte adsorbs, typically by chemi-sorption, i.e., electron transfer, on the surface of the particles to be removed and also on the substrate surface, which enhances electrostatic repulsion between the particles and the wafer surface.
Per [2] Ronay-280, preferred polyelectrolytes are of relatively low molecular weight, typically less than about 100,000, such as 500-10,000, and include a charge-producing functional group. Like said [1] Ronay-490, [2] Ronay-280 indicates that polyelectrolytes contain poly ions, which are macro-molecules having a large number of ionizable groups, and to preserve the electro-neutrality of the polyelectrolyte substance, the poly ion charges must be compensated by counter ions, typically ions of low molecular weight such as H+, Na+, K+ or NH4+. Unlike most uncharged polymers, polyelectrolytes usually are soluble in polar solvents such as water. With regard to their protonation equilibria in aqueous solution, they can be classified as polyacids, as polybases, or as polyampholytes if both acidic and basic groups are present.
Hence, they can contain acidic groups such as carboxyl groups, e.g., poly(acrylic acid), poly(methacrylic acid), poly (methyl methacrylic acid), poly(maleic acid), poly(acrylic acid-co-maleic acid), or saturated or unsaturated poly (carboxylic acids). Also, phosphoric acid and/or sulfonic acid groups can be incorporated into a polymer and may act as acidic functional groups, e.g., per poly(vinyl sulfonic acid). The polyelectrolyte can contain basic groups including nitrogen containing groups, such as polymers with amino, amide, imide, vinyl pyridine, piperidine and piperazine derivatives, e.g., per poly(vinyl amine), poly(ethylenimine), and poly(4-vinyl pyridine). Salts and esters of the foregoing are also contemplated.
Besides the particular compounds 1. to 7. noted in said [1] Ronay-490, per [2] Ronay-280, the following further compounds are contemplated, wherein the repeat number n of the monomer unit is preferably 5-200, and Y is OC1-C4 alkyl (i.e., alkoxy of 1-4 C-atoms), OH− or alkali metal ion such as said Na+, K+ and NH4+ ion.                8. salts or esters of poly(acrylic acid)[—CH2—CH(COY)—]n        9. salts or esters of poly(methacrylic acid)[—CH2—CH(CH3)(COY)—]n        
[3] U.S. Pat. No. 6,019,670, issued Feb. 1, 2000 to Cheng et al. (“[3] Cheng-670”), which is incorporated by reference herein, discloses a CMP apparatus including a carrier for mounting a substrate (i.e., a semiconductor wafer) to be polished, and an opposing polishing pad maintained in moving contact with the wafer mounted on the carrier, e.g., under an applied down force of 2-10 psi, while the carrier and polishing pad are each rotated at 30-200 rpm. The polishing pad is periodically conditioned, i.e., to remove collected debris (glazing) therefrom consequent CMP of such wafers, e.g., using a slurry containing a reactive agent (e.g., deionized water for oxide polishing), abrasive particles (e.g., silicon dioxide for oxide polishing) and a chemically reactive catalyzer (e.g., potassium hydroxide for oxide polishing).
The polishing pad can be a two layer pad in which the upper layer is harder than the lower layer and can be a fixed abrasive pad or a non-fixed abrasive pad. If it is a non-fixed abrasive pad, typically the upper layer is composed of polyurethane mixed with a filler material and is about 50 mils thick, while the lower layer is composed of compressed felt fibers leached with urethane and also about 50 mils thick. On the other hand, if the polishing pad is a fixed abrasive pad, typically the upper layer is a 5-200 mil thick abrasive composite layer composed of abrasive grains held in a binder material, while the lower layer is a 25-200 mil thick backing layer composed of polymeric film, paper, cloth, a metallic film, or the like.
Said [3] Cheng-670 notes that fixed abrasive polishing pads are described in [4] U.S. Pat. No. 5,152,917, issued Oct. 6, 1992 to Pieper et al. (“[4] Pieper-917”); [5] U.S. Pat. No. 5,342,419, issued Aug. 30, 1994 to Hibbard (“[5] Hibbard-419”); [6] U.S. Pat. No. 5,368,619, issued Nov. 29, 1994 to Culler (“[6] Culler-619”); and [7] U.S. Pat. No. 5,378,251, issued Jan. 3, 1995 to Culler et al. (“[7] Culler-251”); which are discussed below.
[4] U.S. Pat. No. 5,152,917, issued Oct. 6, 1992 to Pieper et al. (“[4] Pieper-917”), which is incorporated by reference herein, discloses a coated abrasive article in the form of a backing, e.g., of polymeric film such as polyester film, or of a paper, cloth, metallic film, vulcanized fiber, and/or nonwoven, substrate, bearing abrasive composites of abrasive grains dispersed in a binder serving as medium for dispersing the abrasive grains and for bonding the abrasive composites to the backing. The abrasive grains include, e.g., aluminum oxide, silicon carbide, alumina zirconia, garnet, diamond and cubic boron nitride, e.g., of 0.5-1000, preferably 1-100, micron particle size. The abrasive composites have a predetermined, e.g., pyramid, prism, curvi-linear or saw toothed, shape and are disposed in a predetermined array having a non-random, e.g., repetitive, pattern.
The coated abrasive article is prepared by providing a slurry, e.g., preheated to 40-90° C., of a mixture of a radiation curable or gellable binder and the abrasive grains on the backing located on a production tool, so as to form such abrasive composites of the desired predetermined shape, and at least partially curing or gelling the binder by radiation energy before removing the backing from the production tool, and finally curing the binder, i.e, polymerizing the binder to solid state. The polymeric film forming the backing can be primed with a material such as polyethylene acrylic acid to promote adhesion of the abrasive composite thereto (col. 4, lines 13-22).
Usable binders include phenolic resins, amino plast resins, urethane resins, epoxy resins, acrylate resins, acrylated isocyanurate resins, urea-formaldehyde resins, isocyanurate resins, acrylated urethane resins, acrylated epoxy resins, and/or glue. Particular usable curable binder resins are enumerated (col. 5, line 3, to col. 6, line 20; col. 10, lines 1-24; and col. 11, lines 3-30). The weight ratio of abrasive grains to binder is about 4-1, preferably 3-2, parts abrasive grains to 1 part binder.
As the coated abrasive article is used to erode a surface, the composite breaks down revealing unused abrasive grains, i.e., the abrasive grains are sloughed off and new abrasive grains are exposed. The spaces between the abrasive composites provide means for escape of the swarf (i.e., material removed from the work piece being abraded) from the abrasive article, thereby reducing loading and the amount of heat build up during use.
[5] U.S. Pat. No. 5,342,419, issued Aug. 30, 1994 to Hibbard (“[5] Hibbard-419”), which is incorporated by reference herein, discloses an abrasive composite of (e.g., about 20-95%) abrasive particles in a binder (e.g., about 3-78%, of cured, gelled or polymerized) addition polymerized resin having (e.g., about 1-50%) clay particles dispersed therein. The composite is adhered to a substrate, i.e., backing, such as a paper, cloth, polymeric film or nonwoven backing. The clay particles allow the binder, and thus the composite, to erode controllably upon abrasion of a work piece and expose fresh abrasive particles.
Usable binders include ethylenically unsaturated resins such as acrylated urethane resins, styrene, divinyl benzene, vinyl toluene, amino plast resins having pendant unsaturated carbonyl groups, isocyanurate resins having at least one pendant acrylate group, and isocyanate resins having at least one pendant acrylate group, including a combination of the triacrylate of tris (hydroxy ethyl) isocyanurate and trimethylol as well as epoxy resins. Particular usable resins, including acrylate reactive diluents, are enumerated along with usable polymerization initiators (col. 4, lines 11-32; col. 4, line 60, to col. 5, line 8; col. 8, lines 34-46; col. 10, line 31, to col. 13, line 25; and col. 20, lines 20-25).
[6] U.S. Pat. No. 5,368,619, issued Nov. 29, 1994 to Culler (“[6] Culler-619”), which is incorporated by reference herein, discloses abrasive articles made from slurries of a binder precursor, i.e., polymerizable (curable) resin such as an addition polymerizable resin, abrasive particles and sufficient modifying silica particles to reduce the slurry viscosity.
Usable addition polymerizable resins include styrene, divinyl benzene, vinyl toluene and amino plast resins having pendant unsaturated carbonyl groups, isocyanurate resins having at least one pendant acrylate group, acrylated urethane resins, epoxy resins, and isocyanate derivatives having at least one pendant acrylate group, and especially wherein the isocyanurate resin having at least one pendant acrylate group is the triacrylate of tris (hydroxy ethyl) isocyanurate dissolved in trimethylol propane triacrylate. A reactive diluent can also be present including N-vinyl pyrrolidone, hexane diol diacrylate, triethylene glycol diacrylate, and trimethylol propane triacrylate (col. 9, line 57, to col. 10, line 13), plus a filler including sodium sulfate (col. 14, lines 1-10). Particular usable binder precursors (curable resins) are enumerated along with usable polymerization initiators (col. 7, line 54, to col. 11, line 40; and col. 18, line 10, to col. 19, line 35).
[7] U.S. Pat. No. 5,378,251, issued Jan. 3, 1995 to Culler et al. (“[7] Culler-251”), which is incorporated by reference herein, discloses an abrasive article formed of a backing on which an adhesive coating is bonded, the coating comprising a homogeneous mixture of abrasive particles, a binder, i.e., an organic polymerizable resin such as one comprised of polymer units of trimethylol propane triacrylate and a triacrylate of tris (hydroxy ethyl) isocyanurate, which serves to bond the coating to the backing, and a grinding aid consisting of a halide salt such as cryolite or potassium tetrafluoroborate as well as sodium chloride, potassium chloride and magnesium chloride, and an organic halide compound such as polyvinyl chloride (col. 8, lines 30-43). Particular usable binder resins are enumerated along with usable polymerization initiators (col. 5, line 34, to col. 8, line 4; col. 11, lines 20-46; and col. 15, lines 9-33).
[8] U.S. Pat. No. 5,958,794, issued Sep. 28, 1999 to Bruxvoort et al. (“[8] Bruxvoort-794”), which is incorporated by reference herein, discloses comprehensively the CMP of a semiconductor wafer surface, e.g., of silicon dioxide, by moving contact with a fixed abrasive article, e.g., a polishing pad, which can be erodible, and which has a three dimensional textured abrasive surface that includes a plurality of abrasive particles and a binder in a predetermined pattern. The CMP is effected in the presence of a liquid having a pH of at least 5 such as water, e.g., an aqueous medium containing a metal hydroxide such as potassium hydroxide, sodium hydroxide, or ammonium hydroxide, or a basic compound such as an amine, where the wafer surface being polished contains a metal oxide such as silicon dioxide (col. 12, lines 38-62), and which may contain additives such as lubricants including glycol ethers, glycerine, polyvinyl acetate, polyvinyl alcohols, and ethylene oxide polymers, (col. 13, lines 23-30).
The fixed abrasive article has a backing such as a polymer film, with a surface comprising such abrasive particles, e.g., of ceria, etc. (col. 19, lines 14-30) and a binder in the form of an abrasive coating. The binder can be a thermoset organic polymer resin, and particularly an acrylate or methacrylate polymer resin, and can contain, e.g., 25-75% of, a plasticizer, such as a phthalate ester or derivative thereof, and particularly polyethylene glycol, polyvinyl chloride, dibutyl phthalate, polyvinyl acetate, and polyvinyl alcohol (col. 27, lines 48-67), to increase the erodibility of the fixed abrasive article. The binder can also be in the form of a ceramer binder that includes colloidal metal oxide particles in an organic polymer resin (col. 2, lines 58-60).
Additives can be included in the binder resin such as a surfactant, e.g., polyalkylene oxide (col. 20, line 66, to col. 21, line 10); a filler, e.g., a metal sulfate such as sodium sulfate (col. 21, lines 46-61), or a halide salt such as sodium chloride, potassium chloride or magnesium chloride (col. 22, lines 8-12); an emulsifier such as a quaternary ammonium salt or triethyl amine (col. 25, lines 24-28); expanding agents such as ammonium bicarbonate, sodium bicarbonate, dinitro penta methylene tetramine, or azodicarbonamide (col. 29, lines 42-45); and lubricants such as glycol ethers or glycerine (col. 30, lines 1-4).
Particular usable binder resins and ceramer binders are enumerated along with usable plasticizers and polymerization initiators (col. 2, lines 56-67; col. 22, line 64, to col. 29, line 21; col. 30, line 28, to col. 34, line 5; and cols. 45-47).
[9] U.S. Pat. No. 5,733,176, issued Mar. 31, 1998 to Robinson et al. (“[9] Robinson-176”), which is incorporated by reference herein, discloses a polishing pad for CMP formed of a molded elastomeric substance with a polishing surface and having voids and optional abrasives, e.g., silica, ceria or zirconia, incorporated therein. The voids are located beneath the polishing surface and contain an end point indicator substance, i.e., a fluid, for producing a detectable signal as abrading of the elastomeric substance, e.g., against a semiconductor wafer, releases the end point indicator, whereby to indicate a worn out polishing pad.
Usable indicator substances in the voids include a color indicator dye, a sound indicator gaseous fluid, e.g., air, a pH indicator fluid, an electrical conductivity indicator fluid, a metal contaminant concentration indicator fluid, a friction coefficient indicating lubricant fluid, and a temperature indicator elastomeric substance.
[10] U.S. Pat. No. 5,855,804, issued Jan. 5, 1999 to Walker (“[10] Walker-804”), which is incorporated by reference herein, discloses a method and apparatus for forming a planar surface on a semiconductor wafer at a desired end point by removing material from the wafer with an abrasive medium, such that as the material is removed, the abrasive medium is inhibited from contacting a first exposed area at the desired end point on the wafer while it still contacts a second area thereon that is not yet at the end point, for continuing the polishing at the second area after the polishing has stopped at the first area.
In particular, the wafer has a hydrophobic stratum and a hydrophilic cover layer on the hydrophobic stratum, with a portion of the hydrophobic stratum being at a level proximate to the desired end point. The step of removing material from the wafer involves pressing the hydrophilic cover layer against a hydrophobic planarizing surface of a polishing pad in the presence of an abrasive slurry and under relative motion between the wafer and pad, while the step of inhibiting contact between the abrasive medium and the first area includes exposing the hydrophobic stratum at the first area to the hydrophobic planarizing surface of the pad such that the hydrophobic stratum and hydrophobic planarizing surface prevent the abrasive slurry from contacting the hydrophobic stratum at the first area.
[11] U.S. Pat. No. 5,919,082, issued Jul. 6, 1999 to Walker et al. (“[11] Walker-082”), which is incorporated by reference herein, discloses the self-limiting (self-stopping) CMP of a surface, e.g., of a semiconductor wafer, using a polishing pad having a first member with an abrasive first material, e.g., a polyurethane or polyphenyl oxide material, containing 15-1000 nm particle size abrasive particles such as SiO2, CeO2, Al2O3, Ta2O5 or MnO2, that is structurally degraded during polishing, and a second member of a second material, e.g., an acrylate polymer such as polyacrylates and polymethyl methacrylates, that is less degradable and less abrasive than the first material but more soluble in a solvent such as HCl/H2O solutions, or such as acetone or isopropyl alcohol, than the first material. Once the desired amount of abrasive is worn from the first member, the second member contacts the wafer and reduces or stops further abrasion of the wafer.
[12] U.S. Pat. No. 5,897,426, issued Apr. 27, 1999 to Somekh (“[12] Somekh-426”), which is incorporated by reference herein, discloses CMP of a substrate, e.g., a semiconductor wafer, with a fixed abrasive polishing pad in the presence of a first polishing liquid, and then with a non-fixed abrasive polishing pad in the presence of a second polishing liquid containing abrasive particles to remove scratch defects created by the fixed abrasive polishing pad, the two polishing liquids being of different pH from each other. The non-fixed abrasive polishing pad is formed of a first layer of polyurethane and a second layer of compressed felt fibers, or is formed of a layer of porometric material.
The fixed abrasive polishing pad is formed of an upper layer of abrasive grains, e.g., fused aluminum oxide, ceramic aluminum oxide, green silicon carbide, silicon carbide, chromia, alumina zirconia, diamond, iron oxide, ceria, cubic boron nitride and/or garnet, held in a binder material on a lower layer (backing) of polymeric film, paper, cloth or metallic film. The binder material is formed from an organic polymerizable resin precursor which is cured to form the binder material, the resins including phenolic resins, urea-formaldehyde resins, melamine formaldehyde resins, acrylated urethanes, acrylated epoxies, ethylenically unsaturated compounds, amino plast derivatives having at least one pendant acrylate group, isocyanurate derivatives having at least one pendant acrylated group, vinyl ethers and/or epoxy resins (col. 4, line 63, to col. 5, line 5).
Like said [3] Cheng-670, [12] Somekh-426 also notes that fixed abrasive polishing pads are described in [4] U.S. Pat. No. 5,152,917, issued Oct. 6, 1992 to Pieper et al. (“[4] Pieper-917”); [5] U.S. Pat. No. 5,342,419, issued Aug. 30, 1994 to Hibbard (“[5] Hibbard-419”); [6] U.S. Pat. No. 5,368,619, issued Nov. 29, 1994 to Culler (“[6] Culler-619”); and [7] U.S. Pat. No. 5,378,251, issued Jan. 3, 1995 to Culler et al. (“[7] Culler-251”); which are discussed above.
[13] U.S. Pat. No. 5,972,792, issued Oct. 26, 1999 to Hudson (“[13] Hudson-792”), which is incorporated by reference herein, discloses CMP of a semiconductor wafer using a fixed abrasive polishing pad in the presence of an abrasive-free planarizing solution that oxidizes a surface layer, e.g., a metal layer, of the wafer without passing it into solution, i.e., forms a rough, scabrous layer of non-soluble oxides, such that the fixed abrasive polishing pad removes the oxidized surface layer. The polishing pad is formed of abrasive particles dispersed in a suspension medium and fixedly attached to the suspension medium.
[14] U.S. Pat. No. 5,782,675, issued Jul. 21, 1998 to Southwick (“[14] Southwick-675”), which is incorporated by reference herein, discloses an apparatus and method for refurbishing a fixed abrasive polishing pad used for planarizing CMP of a layer of a semiconductor wafer, by moving contact between the polishing pad and a refurbishing brush to remove polishing waste material therefrom without abrading or otherwise damaging the raised features on the fixed abrasive pad, while supplying a conditioning solution to the pad which interacts with the polishing waste material to effect its removal from the pad.
For example, when the layer being planarized is of poly silicon, a conditioning solution of ammonium hydroxide or tetramethyl ammonium hydroxide is usable for removing poly silicon waste material, and when such layer is of metal, a conditioning solution of hydrogen peroxide, potassium iodate, ferric nitrate, bromide, or other solution having a pH of less than 5 is usable.
[15] U.S. Pat. No. 5,972,124, issued Oct. 26, 1999 to Sethuraman et al. (“[15] Sethuraman-124”), which is incorporated by reference herein, discloses a method of cleaning a semiconductor wafer topography that has been polished by CMP technique with a fixed abrasive polishing pad formed of a polymer based matrix entrained with abrasive particles, by applying a cleaning solution of an acid and a peroxide or an acid oxidant to the topography so as to remove waste particles therefrom including abrasive particles such as cerium oxide, cerium dioxide, alpha alumina, gamma alumina, silicon dioxide, titanium dioxide, chromium oxide or zirconium oxide, derived (dislodged) from the fixed abrasive pad during the prior polishing.
Per [15] Sethuraman-124, it is noted that adhesion forces between dielectric surfaces (e.g., silicon dioxide) and the abrasive particles (e.g., CeO2) are quite strong, such that the particles particularly adsorb on dielectric surfaces, it being believed that a high zeta potential, i.e., electric static or charge difference, exists between the particles and the dielectric, causing the particles to “stick” to the dielectric (col. 2, lines 56-61).
Per [15] Sethuraman-124, it is further noted that where the polishing liquid used for the underlying fixed abrasive polishing pad CMP of the wafer is an acidic liquid, a silicon nitride layer can act as a polish stop while polishing an oxide layer formed over the silicon nitride layer, e.g., in effecting a shallow trench isolation operation, in that a polish selectivity of oxide to nitride greater than 20:1 may be achieved by adjusting the acidic liquid pH to between about 6.0 and 7.0, it being postulated that the reaction rate between the acidic liquid and the oxide is substantially greater than that between such liquid and the nitride (col. 6, lines 7-28).
It is desirable to provide a polishing pad for CMP of a surface of a semiconductor wafer, having a polishing layer of friction erodible binder material containing both abrasive particles and an electrolyte substance such as a polyelectrolyte to enhance the CMP operation, wherein the binder material is incrementally eroded and in turn the abrasive particles and electrolyte substance are incrementally released into direct contact with the wafer surface being planarized.